EVALUATION OF THE EFFECT OF ANIONIC POLYACRYLAMIDES …

Petroleum & Coal

ISSN 1337-7027

Available online at www.vurup.sk/petroleum-coal

Petroleum & Coal 57(5) 403-411, 2015

EVALUATION OF THE EFFECT OF ANIONIC POLYACRYLAMIDES ON STABILITY

AND DISCHARGE OF FOAM INJECTION INTO OIL RESERVOIRS WITH

DIFFERENT CHARACTERISTICS IN ENHANCED OIL RECOVERY

Hassan Tabe’Bordbar1, Seyyed Saeed Ghorashi2

1Polymer Engineering Department, Arak University, Arak, Iran;2Research Institute of

Petroleum Industry, Tehran, Iran;Corresponding Author email: [email protected]

Received July 7, 2015; Accepted September 14, 2015

Abstract

In this study the effect of anionic polyacrylamides on stability and discharge of foam injection into oil reservoirs with different characteristics in enhanced oil recovery was evaluated. As the Iranian reservoir formations are unique and few works has been done in this field, particular experiments must be carried out to enhance oil recovery. The efficiency of oil recovery with foam injection method, foams Stability with injection in porous media, effects of adding polymer to the foam formulation and the foam discharge

was evaluated. The polymers used to increase the foam stability, were two types of anionic polyacryl-

amides, AN-105 with anionic degree (molar degree) of 5% and AN-125 with anionic degree of 25%. Two types of surfactants, SLES and NP30 were used. Two samples of F and S Brine water were used to prepare the foam. It was concluded that the polymer with higher molecular weight and anionic degree, had the best effect on foam stability. Also it was concluded that the salt sensitivity of foam would be decreased by increasing the amount of gas. Increasing the polymer concentration decreased the output rate of foam. AN125 increased the foam stability more than AN105 and as the salinity increased, the

discharge rate increased.

Keywords: anionic polyacrylamides; surfactant; gas; foam stability; foam discharge; enhanced oil recovery.

1. Introduction

Foam agents are used in various applications in petroleum industries, including drilling, acid

or hydraulic fracturing, gas production, blocking condense fluid flows and recovery processes.

Surfactants are used to produce foam in low concentrations. Foams are used as mobility control

agents in various processes such as secondary recovery and steam injection, CO2 and nitrogen

injection to improve performance. Surfactants and certain formulations are needed to produce

foams to tolerate oil and electrolytes and can be stable at reservoirs pressure and tempera-

ture [1]. Foams have more effective viscosity than gas; therefore, they are used as a method

to improve the sweeping efficiency of gaseous processes such as steam and CO2 injection.

Viscous fingering and gas overriding that caused by low viscosity and density of gas, can be

reduced by means of foams. In a heterogeneous formation, preferably fluids flow in layers

with high permeability and foam creates there and local resistance to flow increases strongly, thus

the injected fluids are deviated to low permeable areas and process efficiency improves [2].

Also in water sweeping process, water moves from high permeable areas of the reservoir

and reaches to the well, it reduces oil production and water sweeping will not be effective.

Using foams is a useful method to reduce water production in water sweeping [3].

Gas mobility will decreases by injecting surfactants which can produce foam, which in turn

reduces viscous fingering, gas overriding and transition to high permeable layers. The foam

traps the gas, increases the gas saturation degree and decreases the oil saturation degree.

The foam can also affect the movement of fluid and reduce it. Gas in the foam is surrounded

by a thin layer of fluid. Thin layer of foam creates cavities in the gas flow by contacting with

the wall. A part of the gas could be held by immovable lamellas that block some of the flow

paths. Correspondingly reducing the gas flow paths reduces the gas relative permeability.

However, the actual viscosity of the gas remains unchanged and the gas shows an increase

in apparent viscosity due to a decrease in the flow velocity [4]. The fluid behaves differently

from the gas in presence of foam. Flow paths join together through the lamellas. During the

foam growth, gas saturation degree increases and acts as an extra rock matrix by blocking

the fluid flow. The relative flow permeability decreases by reducing flow paths. In other words,

increase in gas saturation degree, affects the relative fluid permeability and decreases the fluid

saturation degree [5].

ASP formulation has been used extensively in almost empty old reservoirs. Polymers are

used in ASP process to reduce mobility. Polymers have some disadvantages:

1) High molecular weight polymers are large and may block rocks.

2) Polymers may be unstable at high temperatures and salinity.

3) High flow speed may damage the foam [2].

In a study by Srivastava [11], the polymer has replaced with gas to produce the foam.

Core flooding was carried out successfully on sandstone and dolomite with low to moderate

permeability using alkaline - surfactant - gas (ASG). By using negative salinity gradient, It

has been able to mobilize the trapped surfactant and increase foam stability to improve the

mobility ratio and to control the conformance during running forward [6-7]. Choosing an appro-

priate foam agent to reduce the mobility in gas flooding operations needs to sift many surfac-

tants. Several methods for evaluating foams have been mentioned by researchers. Foams

stability is measured commonly in three ways:

1) Determine the life time of bubbles.

2) Determine the foam volume at steady state (dynamic) under certain conditions of the gas

flow, vibrating or cutting actions.

3) The vanishing rate of the foam column (static) [8].

Repeatability of the first method is difficult because of strong impact of small pollutions or

vibrations. The other two methods are used however producing and disappearing the foam is

not always monotonous. Dynamic method is the most appropriate one for measuring foams

that disappear fast because of their short life time. Static foam tests are done for more stable

foams. In a dynamic test, the foam is created with passing the gas flow through a porous inlet

into the solution, if the inlet gas flow to the column remains constant, the foam volume will

be constant and can be measured. These tests can be done by several methods such as standard

ASTM tests [7]. These techniques are often used to determine the stability of foams that are

gradually disappear. Other methods to determine the foam stability include displaying the

physical properties of the foam. Several researchers used NMR spectroscopy and MRI imaging to

investigate the foam stability [10].

In this study the effect of anionic polyacrylamides on stability and discharge of foam injected

into oil reservoirs with different characteristics in enhanced oil recovery was evaluated. As

the Iranian reservoir formations are unique and few works has been done in this field, particular

experiments must be done to enhance oil recovery.

2. Experimental study

2.1 Materials and equipment

For foam stability tests, the polymers used to increase the foam stability, were two types

of anionic polyacrylamides, AN-105 with anionic degree (molar degree) of 5% and molecular

weight of 6 million (g/mol) and AN-125 with anionic degree of 25% and molecular weight of

8 million (g/mol). Two types of surfactants, SLES and NP30 were used. Two samples of F

and S brine water were used to prepare the foam. Salinity degree of S brine water was more

than F brine water. Water samples analysis and their salts and ions quantity, are given in

tables 1 and 2, to prepare the synthetic samples.

H. T. Bordbar, S. S. Ghorashi/Petroleum & Coal 57(5) 403-411, 2015 404

Table 1 The compounds of synthetic F brine water and its salts and ions quantity in pH=4.9

Salt Synthetic brine

water (ppm)

Ion Synthetic brine

water (ppm)

NaCl 10.046 Na+ 3960

KCl 0.053 K+ 28

MgCl2-6H2O 1.219 Ca++ 790

CaCl2-2H2o 2.898 Mg++ 213

MgSO4 0.333 Cl- 7300

NaHCO3 0.030 SO4-- 266

TDS 12900 HCO3- 22

Table 2 The compounds of synthetic S brine water and its salts and ions quantity in pH= 5.1

Salt Synthetic brine

water (ppm)

Ion Synthetic brine

water (ppm)

NaCl 39.6889 Na+ 15730

KCl 0.4577 K+ 240

CaCl2-2H2O 6.4803 Ca2+ 2340

MgCl2-6H2O 2.7828 Mg2+ 400

MgSO4 0.3333 Cl- 29400

NaHCO3 0.4295 SO42- 290

TDS 50800 HCO3- 312

2.2 Test methods

2.2.1 Evaluation the efficiency of oil recovery with foam injection methods

In order to investigate the foam stability with simultaneous injection of gas and liquid

method that is a type of foam injection processes to enhance oil recovery, an appropriate

foaming device was set up. According to Figure 1, in this device, N2 was led to the gas liquid

mixing zone from a capsule by controlling the flow rate Brooks model. On the other hand,

the cylinder containing surfactant and polymer liquid, led the liquid phase to the gas-liquid

mixing zone by HPLC pump Waters-590 model. In simultaneous injection of gas-liquid, the

foam with different volume fraction could be prepared. By changing the flow rate of two

different phases that helped the evaluation of the foam quality. The height of the foam at

the bottom of the scaled column of the device after a certain period of time, determined the

optimum stability of the formulation. According to figure 2, a small cylinder filled with glass

beads with average size of 600 microns in the outlet of the device, was used for

homogenizing the gas-liquid mixture in these tests. If the homogenizing cylinder would not

be used, non-uniform foam according to figure 3 was obtained.

Figure 1 Foam preparation with specific quality system in surrounding pressure and

temperature


Fig. 2 Diagram of the specific foam preparation system with specific quality

Fig. 3 The obtaining foam before connecting homo-genizing factor and homogenizing cylinder that is shown at the figure

2.2.2 Evaluation of foam stability with injection in porous media conditions

The stability of foams prepared with samples of the F and S brine water, the formulation

of surfactants, type and different concentrations of polymers by different volume fraction with

respect to the fluid and gas flow rate were examined. The prepared foams were stored in

scaled cylinders. The foam stability and optimized foam formulation for injection in porous

media were determined by comparing foam heights at the scaled cylinders in different periods

of time. In this experiment according to figure 1, the gas was injected from one side and

liquid containing brine water and optimized surfactant with formulation of 0.2% SLES +

0.3% NP30 was injected from the other side.

2.2.3 Effects of adding polymer to the foam formulation

AN105 and AN125 polyacrylamide polymers were mixed with different flow rates to increase

the foam stability. The filling time of scaled cylinders with foams was 4 minutes. The foams

stability was evaluated at 1, 5 and 30 minutes with determining the height of foams in scaled

cylinders.

2.2.4 Evaluation the foam discharge

Evaluating the foam discharge was considered as continues step after evaluating the foam

stability. Accordingly the sample was observed at different time periods with 1 (mm/min) of

liquid flow rate and 7 (mm/min) of gas flow rate until rising to volume of 50 ml.

3. Results and discussion

The liquid discharge from the foam membrane caused thinning the membrane and gradually

damaging the foam. If the factor which was caused the discharge rate of fluid through the

membrane would be reduced, undoubtedly would affect the stability of the foam. Adding

polymer to the solution increased its viscosity and reduced the liquid discharge from the

membrane, which resulted increasing the foam stability. Using polymer increased the foam

stability and the liquid viscosity, using the polymer with surfactant in oil recovery could have

additional effect on improving the molecular movements. The polymer with higher molecular

weight and anionic degree had the best effect on foam stability. As AN125 has higher molecular

weight and more chain entanglements than AN105, it gave more stable foam as expected.

Thus the calculations and results were based on AN125 properties. The test results were also

in agreement with increasing foams stability. Figure 4 showed the effect of polymer type on

foams stability in distilled water, F and S brine waters. As indicated AN125 had increased

foams stability in F and S brine water. According to figures 5 and 6 it could be seen that the

higher percent of polymer and higher amount of gas, increased foams stability in F brine

water. Based on the results, foams stability for polymer concentrations of 0.075% and 0.1%


were nearly identical. So economically, using less percentage of polymer would be more

appropriate.

Figure 4 The effect of polymer type on foams stability in distilled water and F and S brine waters

Figure 5 The height of foam after 1, 5 and 30 minutes, and different percent of polymer and injection rate of 1ml Liquid + 5 ml gas

Figure 6 The height of foam after 1, 5 and 30 minutes, and different percent of polymer and injection rate of 1ml Liquid + 10 ml gas

It can be seen in figures 7 and 8, that the results were repeated. For S brine water that had

more salinity, using 0.1% of AN125 polymer optimized foams stability and was more economical.

The results of foam discharge can be seen in Figures 9 to 12. It was concluded that the salt

sensitivity of foam would be less by increasing the amount of gas. This was because of the

amount of liquid was less than gas in a certain foam volume. Also with increasing polymer

concentration, the resulting foam was more stable because of increasing the foam solution

viscosity. Increasing the polymer concentration decreased the output rate of foam because

of increasing the viscosity and reducing the power of caring the gas. The optimum polymer

concentration was 0.1% for stability. Increase in polymer concentration, decreased the salt

0

10

20

30

40

DW FW SWH

eigh

t (m

l)

Water Type

AN105

AN125

0

10

20

30

1 min 5 min 30 min

Hei

ght

(ml)

Time (Minute)

0.1 % AN125+FW

0.075 % AN125+FW

0.05 % AN125+FW

0

10

20

30

40

1 min 5 min 30 min

He

igh

t (m

l)

Time ( Min )

0.1 % AN125+FW

0.075 % AN125+FW

0.05 % AN125+FW


sensitivity due to increasing the lamella film thickness. Also the rate of outlet foam reached

to maximum with increasing the amount of gas and then decreased because of damaging

the output foam. AN125 increased the foam stability more than AN105 and as the salinity

increased, the discharge rate increased. The discharge rate decreased a little with increasing

the polymer percent and then increased due to that the liquid phase got heavier and absorbing

forces overcame the bonding forces because of increasing the viscosity.

Figure 7 The height of foam after 1, 5 and 30 minutes, and different percent of polymer and injection

rate of 1ml Liquid + 5 ml gas

Figure 8: The height of foam after 1, 5 and 30 minutes, and different percent of polymer and injection rate of 1ml Liquid + 10 ml gas

0

10

20

30

1 min 5 min 30 min

He

igh

t (

ml)

Time ( min )

0.05% Polymer + SW

0.075% Polymer +SW

0.1% Polymer + SW

0

10

20

30

40

1 min 5 min 30 min

He

igh

t (m

l)

Time

0.05% polymer + SW

0.075% Polymer +SW

0.1% Polymer + SW

0.125% Polymer +SW

Figure 9 Sample discharge with formulation of 0.2% SLES + 0.3% NP30 in distilled water without polymer


Figure 10 Sample discharge with formulation of 0.2% SLES + 0.3% NP30 in S brine water without polymer

Figure 11 Sample discharge with formulation of AN125 0.2% SLES + 0.3% NP30 + 0.1%

AN 125 Polymer in S brine water


Figure 12 Sample discharge with formulation of 0.2% SLES + 0.3% NP30 + 0.1% AN

125 Polymer in distilled water

4. Conclusions

In this study the efficiency of oil recovery with foam injection, foams stability with injection

in porous media conditions, effects of adding polymers to the foam formulation and the foam

discharge was evaluated. It was concluded that the polymer with higher molecular weight

and anionic degree, had the best effect on foam stability. AN125 had increased foams stability

in F and S brine water. The higher percent of polymer and higher amount of gas, increased

foams stability in F brine water. Foams stability for polymer concentrations of 0.075% and

0.1% were nearly identical. So economically, using less percentage of polymer would be more

appropriate. For S brine water that had more salinity, using 0.1% of AN125 polymer optimized

foams stability and was more economical. Also it was concluded that the salt sensitivity of

foam would be less by increasing the amount of gas. The resulting foam was more stable

with increasing polymer concentration. Increasing polymer concentration, decreased the outlet

rate of foam. The optimum polymer concentration was 0.1% for stability. Increase in polymer

concentration, decreased the salt sensitivity. AN125 increased the foam stability more than

AN105 and as the salinity increased, the discharge rate increased.

References

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